Which of the following examples best represents a public good?

A lighthouse protecting boats from a rocky coastline exemplifies a public good due to its two main characteristics: non-excludability and non-rivalry. Once a lighthouse is built, it provides illumination and guidance to all passing boats without being able to restrict access to any specific vessel. This means that no boat can be excluded from benefiting from the light. Additionally, the use of the lighthouse’s light by one boat does not diminish its availability to others; multiple boats can benefit from the guiding light at the same time without reducing its effectiveness.

In contrast, options like a crowded subway system represent a common resource, which can exhibit rivalry when overcrowded, leading to decreased quality of service for users. A personalized tutoring session and a membership to a private gym are both examples of private goods, as they can exclude individuals from accessing these services, and their use is rivalrous—only one person can benefit from the session or membership at a time. Therefore, the lighthouse stands out as the best representation of a public good in this context.